Enhancement of spectral modulation frequency in acoustics and identification of vowels

Abstract

The pattern of intensity variations across audio frequency can be represented as a series of spectral modulation frequencies. Selectivity for spectral modulation frequency in the auditory system has been demonstrated by physiological and psychophysical studies, suggesting that auditory perception of complex sounds might be based on spectral envelope channels. The present study investigated the effects of enhancing spectral modulation frequency on vowel acoustics and vowel identification. Twelve naturally spoken American-English vowels by three female talkers served as the standard stimuli. Various spectral modulation frequency regions of the standard vowels combined with a long-term speech-shaped (LTSS) noise were enhanced. Identification performance for the vowels presented in LTSS noise with and without spectral modulation frequency enhancement was estimated for seven young normal-hearing listeners. Vowels were presented at a sensation level of 3 dB in the LTSS noise (70 dB SPL). Results indicated that vowel identification performance was improved on average by 4%–6% over the 12-vowel categories for spectral modulation enhancement between 1.0 and 2.5 cycles/octave. Acoustic analysis suggested that the improved vowel identification as a result of the global spectral modulation enhancement may be due to increases in the spectral contrast of individual formants.